1. Field of the Disclosure
The present invention relates generally to power converters, and in particular but not exclusively, relates to controllers for switched mode power converters.
2. Background
A wide variety of household or industrial appliances require a regulated direct current (dc) source for their operation. Switch mode power converters are to convert a low frequency (e.g. 50 Hz or 60 Hz) high voltage ac (alternating current) input voltage to the required level of dc (direct current) output voltage. Various types of switch mode power converters are popular for this use because of their well regulated output, high efficiency, small size along with the safety and protection features. Different control methods such as PWM (pulse width modulation), PFM (pulse frequency modulation) or on-off control may be used in controllers for switch mode power converters to regulate the output voltage versus load and line variations.
Switch mode power converters may include a high frequency transformer to provide safety isolation and to transform the voltage level, usually to a lower voltage. The output of the transformer is then rectified and filtered to provide a regulated dc output to be applied to the electronic device. Output regulation in a switched mode power converter is usually provided by sensing the output and controlling the power converter in a closed loop. The output sense could be realized with an extra winding on the transformer core such as a bias, auxiliary or feedback winding, which in some cases may also provide the operating power for the power converter controller. In some switched mode power converters, the feedback or control signal can be provided with an opto-coupler from a sense circuit coupled to the DC output. In some other switched mode power converters, the feedback or control signal could be extracted indirectly from a third winding that is magnetically coupled to the secondary winding on the same transformer core. The feedback or control signal may be used to modulate a duty cycle of a switching waveform generated by the power converter controller or may be used to change switching frequency or by disabling some of the cycles of the switching waveform generated by the power converter controller to control the DC output.
In order to provide specific functions to a power converter controller, additional pins or electrical terminals are added for each function to an integrated circuit of the power converter controller. As a consequence, each additional function that is added to a power converter controller generally translates into an additional pin on the power converter controller chip, which translates into increased costs and additional external components. Another consequence of providing additional functionality to power converter controllers is that sometimes there is a substantial increase in power consumption by providing the additional functionality.